1. Field of the Invention
The present invention relates to a developer supplying device for supplying a developer to a developing device. In addition, the present invention relates to a developing device, which develops an electrostatic latent image with a developer to form a visual image and which uses the developer supplying device. Further, the present invention relates to an image forming apparatus which forms a visual image using the developing device.
2. Discussion of the Background
In conventional electrophotographic image forming apparatus, which have been used for copiers, printers, facsimiles, etc., an electrostatic latent image is formed on an image bearing member (such as photoreceptor drums and belts) according to image information, and the electrostatic latent image is developed with a developing device having a developer bearing member to form a visual image (i.e., toner image) on the image bearing member. In this regard, two-component developing devices using a two-component developer including a toner and a carrier are broadly used as the developing device because of having advantages such that toner images having good transferability, and half-tone reproducibility can be stably produced even when environmental conditions such as temperature and humidity vary.
Two-component developing devices develop electrostatic latent images using a developer including a toner and a carrier. In this case, only the toner is used for forming visual images. Therefore, it is necessary to supply the toner to the developing devices as the amount of toner included in the developer decreases. In this regard, replaceable toner containers (such as bottles) are typically used for supplying toner. Among various toner containers, toner bottles having a spiral groove on a surface thereof are broadly used because of having a good combination of toner supplying stability and toner feeding efficiency.
Among such toner bottles having a spiral groove, the following toner bottle is well known. Specifically, the toner bottle has a cylindrical main body, a closed bottom portion formed on one side of the main body, and a narrowed mouth portion which is provided on the side of the main body opposite to the bottom portion and from which a toner is to be discharged. A continuous spiral group is formed on an inner surface of the main body while extending from the bottom portion to the mouth portion so that when the toner bottle is rotated, the toner in the bottle is fed to the outside through the mouth portion. In addition, a projection is formed at a position of the outer surface of the bottom portion apart from the central axis of the bottle so that a rotating force is transmitted to the toner bottle via the projection. Since the toner in the toner bottle is moved to the exit (i.e., the mouth portion) as the toner bottle is rotated, the toner can be stably supplied. The toner thus supplied from the toner bottle is guided to a developing device by means of a screw or free-fall of the toner due to gravity.
When development operations are repeatedly performed for a long period of time using a two-component developer, a problem in that the coating layer of the carrier in the developer is abraded or components of the toner adhere to the coating layer, resulting in deterioration of the charging ability of the carrier is caused. In this case, a background development problem such that images whose background area is soiled with the toner are produced, and a toner scattering problem in that the toner is scattered around the developing device, resulting in contamination of the parts of the image forming apparatus are caused. Therefore, the developer has to be replaced with a fresh developer at certain intervals.
In attempting to solve the problems (i.e., to prevent deterioration of developer and to prolong the developer replacement interval), a supplementary developer supplying method in which a mixture of a toner and a carrier is supplied to a developing device while discharging an excess of the developer in the developing device to gradually replace the carrier with a fresh carrier is used now. There is a developer supplying device using this supplementary developer supplying method, which includes a developer container, part or entire of which is deformable, and a pump which sucks the developer contained in the container together with air to feed the developer to a developing device.
When no developer remains in a developer bottle in such image forming apparatus, the image forming apparatus judges that the developer is exhausted and requests a user to replace the developer bottle, in order to prevent occurrence of a toner concentration decreasing problem. In this regard, many image forming apparatus indicate that the developer is in a near-end state for safety before such developer-end judgment.
FIG. 15 is a graph showing the relation between the amount of residual developer and developer feeding capacity of a developer supplying device. It can be understood from FIG. 15 that the developer feeding capacity starts to decrease when the amount of residual developer is about 300 g, and thereafter the developer feeding capacity decreases in proportion to the amount of residual developer. It can be understood from this graph that the method for determining the amount of residual developer only from the developer feeding time (see JP-A 2000-338767) is difficult particularly when the developer is in a near-end state.
A direct optical detection method such that the fed toner is directly detected with an optical sensor is used for determining the amount of fed toner. In this method, a detection window is provided in a toner passage of a toner feeding member, and a glass tube is provided inside the detection window while setting an optical sensor outside the detection window to detect whether the toner is present in the glass tube. The detection results are used for judging whether the toner is exhausted. However, this method has a drawback in that when the glass tube tends to be contaminated with the toner, and thereby misdetection is caused.
The above-mentioned method proposed by JP-A 2000-338767 in which the amount of residual toner is determined depending on the integration value of the toner supplying time is not accurate when the toner is in a near-end state because the toner feeding amount largely varies at the toner near-end. In addition, as illustrated in FIG. 15, when the amount of residual toner is small, the amount of toner fed from the toner bottle per a unit time decreases. Therefore, the amount of residual toner cannot be precisely determined from the integration value of the toner supplying time at the toner near-end.
For these reasons, the inventor recognized that there is a need for a developer supplying device, which can precisely determine the amount of residual developer in a developer container.